Several aspects of gene structure and function are being studied in cultured cell lines and organ cultures from Drosophila melanogaster, in situ hybridization experiments with polytene chromosomes are being used to analyze populations of cytoplasmic messenger RNA and to compare them with the heterogeneous nuclear RNA in the cells. We have chosen two sets of coordinated gene responses, "heat shock" and the ecdysone triggering of differentiation, for especial study. Both of these gene responses can be experimentally induced and both can, we believe, serve as model systems for the kinds of changes in genetic activity that occur during cell determination and differentiation in higher organisms. In addition there is reason to believe that the "heat shock" response is a general homeostatic mechanism in insects. We intend to analyze RNA metabolism at all stages and to search for genetic control points throughout the lifetime of the RNA. In addition we will attempt to relate the cytoplasmic messenger RNAs induced in our experiments to specific proteins so that the relation between gene induction and cell phenotype can be studied in these systems. BIBLIOGRAPHIC REFERENCES: Lengyel, J.A. and Pardue, M.L. Analysis of hnRNA made during Heat Shock in Drosophila Melanogaster Cultured Cells. J. Cell. Biol. 67: 240a (1975). Bonner, J.J. and Pardue, M.L. The Effect of Heat Shock on RNA Synthesis in Drosophila Tissues. Cell 8: 45-50 (1976).